In order to study the genetic causes of sterility in azoospermia and severe oligospermia, we investigated the sequences of the SRY(sex determining region of Y chromosome) gene that is known to determine the maleness of human. A 609 bp fragment of SRY open reading frame, containing the entire known SRY, was amplified from genomic DNA with primers XES2 and XES7. It was amplified from genomic DNA of one normal man, three azoospermic man and four severe oligospermic man. These amplified DNAs were subcloned for DNA sequencing. In this study, we found that normal, azoospermic and severe oligospermic men had the base of thymine at 155th codon region, while SRY sequence study by Sinclair et al. (1990) showed the base of cytosine. As a result, C→T transition mutation at 155th codon in SRY gene coding region had occurred but there was no change in the amino acid sequence [serine (AGC)→serine(AGT)]. It seems that the polymorphism in the coding region of SRY gene was found in Korean population for the first time.